Electronic bed weighing vs daily fluid balance changes after cardiac surgery.

Objective: The purpose of this study is to establish the validity and reliability of measuring weight in critically ill patients with electronic weighing beds.

Methods: All patients admitted to a private intensive care unit (ICU) after cardiac surgery over a 7-month period were weighed on admission and then twice daily (1200 and 2400 hours) using electronic weighing beds (Hill-Rom, Batesville, AR). For each measurement, nonremovable items were recorded, and an average value was deducted from measured weight. We compared differences in body weights (BWs) between 2 consecutive 12-hour periods with the corresponding fluid balance (FB). In addition, we compared weights obtained with electronic weighing beds with those obtained with a regular calibrated scale on ICU discharge.

Results: We obtained data in 103 patients for 414 (75.5%) of 548 of all possible BW measurements. On average, we identified a total of 3.5 kg (SD, 1.4) of nonremovable items on patients' beds. The correlation between 12-hourly changes in BW and FB was weak (r = 0.28; 95% confidence interval [CI], 0.17-0.39), even after correction for insensible fluid losses (r = 0.27; 95% CI, 0.15-0.38) and when only values obtained in intubated patients were taken into account (r = 0.34; 95% CI, 0.16-0.49). Similarly, limits of agreements were wide (95% CI, -3.3 to 3.5 kg). There was also poor agreement between weights obtained on electronic beds and those obtained on the regular scale on ICU discharge (95% CI, -7.6 to 7.6 kg).

Conclusions: Body weight measured by electronic weighing beds does not seem sufficiently robust or accurate to replace daily FB in ICU. The clinical value of purchasing such beds remains uncertain.